Correlations Between Transverse Coefficients In Magnetic Topological Materials Mn₃Ge And Co₂MnGa

Anomalous Hall effect along with its thermoelectric and thermal counterpart,anomalous Nernst effect and anomalous thermal Hall effect,have attracted lots of attentions in the field of condensed matter physics since observed.Recently,it has been widely believed that the anomalous transverse responses observed in magnetic topological materials originate from the nontrivial Berry curvature in moment space.However,the correlations between these anomalous coefficients have not yet been studied systematically.Based on magnetic topological materials Mn₃Ge and Co₂MnGa,we discussed the correlation between anomalous Hall conductivity and anomalous thermal Hall conductivity in Mn₃Ge,and we explored the experimental scaling law between anomalous thermoelectric and anomalous Hall con-ductivity in different magnetic topological materials,and we also investigated the planar Hall effect and its memory effect induced by the nontrivial antiferromagnetic domain walls.The main results and conclusions are summaried as following:（1）We present a comprehensive study on electric and thermal transport in non-collinear antiferro-magnetic Mn₃Ge from room temperature down to dilution refrigerator temperature range,to study the temperature dependent anomalous Wiedemann-Franz ratio.We found that,between 0.3 K and 100 K,the anomalous Hall conductivity and anomalous thermal Hall conductivity obey the Wiedemann-Franz law.These results confirm that the anomalous Hall effect in Mn₃Ge originates from the nontrivial Berry curvature in the moment space.On the other hand,we found our results departure Wiedemann-Franz law above 100 K.We argue that the finite-temperature violation of the Wiedemann-Franz law is caused by a mismatch between the thermal and electrical summations of the Berry curvature instead of by inelastic scattering.This interpretation was backed by our theoretical calculations,which reveal a competition between the temperature and the Berry curvature distribution.Besides,we checked the anomalous Bridgman relation in Mn₃Ge by measuring the temperature dependent anomalous Nernst effect and Ettingshausen effect.（2）By measuring Hall effect and thermal Hall effect,We studied the anomalous Wiedemann-Franz ratio in the Heusler Weyl ferromagnet Co₂MnGa.We also summarized the experimental scaling law between anomalous thermoelectric conductivity and anomalous Hall conductivity in different topo-logical materials,based on the studies of Mn₃Ge and Co₂MnGa.Firstly,we checked the anomalous Wiedemann-Franz law,linking electric and thermal responses,over the whole temperature window in Co₂MnGa.This indicates that the anomalous Hall effect has an intrinsic origin and the Berry spectrum is smooth in the immediate vicinity of the Fermi level.Scrutinizing all topological magnets explored previously,we observed that this ratio is sizable fraction of k_B/e at room temperature.We provided a qualitatively explanation for this feature by means of semiclassical picture and Mott relation.（3）By tuning the magnetic field and cycling temperature,we studied the planar Hall effect caused by the nontrivial antiferromagnetic domain walls in Mn₃Ge.We observed that the planar Hall effect extended from Néel temperature down to 2 K,and found that the memory-like planar Hall effect can be wiped out if the prior magnetic field exceeds 0.8 T or when the temperature exceeds Néel temperature.We also found a detectable difference of the amplitude of planar Hall resistivity between zero-field thermal cycling and field thermal cycling.According to the research in this thesis,we confirmed that the anomalous Hall effect,anoma-lous Nernst effect,and anomalous thermal Hall effect originate from the Berry curvature in Mn₃Ge and Co₂MnGa,and we found a new mechanism of breaking the Wiedemann-Franz law at high tem-perature,and summarized that the ratio of anomalous thermoelectric conductivity to anomalous Hall conductivity closes to k_B/e in different magnetic topological materials.These studies enrich our un-derstanding to the electric,thermoelectric,and thermal transportation.